The present invention relates to devices for injecting, administering, infusing, dispensing or delivering a substance, and to methods of making and using such devices. More particularly, the invention relates to an injection device for administering a liquid product, e.g. a medicine.
In known injection devices, a liquid product situated in a product container is delivered by a force which acts on a piston arranged in the product container such that it can be shifted. The force is transmitted via the piston onto the liquid, such that the latter is delivered via an opening in the product container, wherein the piston is generally shifted in the direction of the opening. Biased springs which act on the piston are often used to generate the force. The problem with such biased springs is that the spring force decreases as the spring relaxes, in accordance with the path or travel. To be able to determine, in the case of injection devices, whether a product is in the process of being delivered or has been completely delivered, signals can be generated during the advancing movement of the piston, for example by a relative movement being performed between a catch and an engaging element, such that clicking sounds are emitted as the catch is crossed. However, the emitting of clicking sounds can be misleading for users of such devices, since the spring force, which is variable over the spring path, causes irregularities in the emission of clicking sounds.